This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Field of the Invention
The present disclosure relates to the field of hydrocarbon recovery operations. More specifically, the present invention relates to rotary steerable drilling systems and methods for use of rotary steerable devices for the formation of boreholes in an earth formation.
Technology in the Field of the Invention
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. In most instances, the drill bit is rotated in response to torque that is applied to the drill string at the drilling rig. The rotational force applied to the drill string is transmitted to the drill bit in order to impart a grinding force against the rock face downhole. Such a process is commonly used in vertically-completed wellbores, and is referred to as “rotary drilling.”
In conventional rotary drilling operations, the drilling rig rotates a drill string comprised of tubular joints of drill pipe connected end-to-end. The drill bit is connected to the lower end of the drill string.
In some instances of rotary drilling, the drill bit is part of a bottom hole assembly that includes mud motors. During drilling operations, a drilling fluid, commonly referred to as drilling mud, is pumped down the interior bore of the drill pipe, across the mud motors, through the drill bit, through an annular region formed between the drill string and the surrounding formation, and back to the surface. In this instance, the mud motors are used to rotate the drill bit without rotation of the drill string.
In wellbores that are deviated or horizontally-completed, a special bottom-hole assembly is employed. The bottom-hole assembly allows the operator to control or “steer” the direction of the bit. This is commonly done by applying an eccentric force to the drill bit, causing the rock face to be cut along a desired azimuth. Such an operation is referred to as “directional” drilling.
In directional drilling, pressurized mud is pumped down the interior of the drill string and is used to power the mud motors. The mud motors, in turn, are mechanically coupled to and turn the nearby drill bit. The mud motors are used with stabilizers or bent subs to impart an angular deviation to the drill bit. This, in turn, deviates the well from its previous path and in the desired azimuth and/or inclination.
There are several advantages to directional drilling. These primarily include the ability to complete a wellbore along a substantially horizontal axis of a subsurface formation, thereby exposing a substantially greater formation face. A formation fracturing operation may be conducted to further expose the formation to the wellbore. Advantages also include the ability to penetrate into subsurface formations that are not located directly below the wellhead. This is particularly beneficial where an oil reservoir is located under an urban area or under a body of deep water. Another benefit of directional drilling is the ability to group multiple wellheads on a single platform, such as for offshore drilling. Finally, directional drilling enables multiple laterals and/or sidetracks to be drilled from a single wellbore in order to maximize reservoir exposure and recovery of hydrocarbons.
Directional drilling is generally performed using downhole rotary steerable drilling systems, or “RSS.” In the oil and gas industry, a select few companies compete in the RSS market. These companies generally represent large service companies, although a few smaller companies are currently in operation. None of these companies actually sell their RSS equipment; rather, they provide the equipment at the drill site and oversee the drilling operation as a service. Once the wellbore is formed and the well is completed, the engineers return to their base and store their RSS tools for later use.
The known bottom hole assemblies used for RSS each include a steering unit. The steering units operate with dedicated control electronics to change a force orientation of the drill bit as the formation is penetrated. Modern RSS systems attempt to achieve a high bend angle, or high dog-leg severity ratio (“DLS”), through the steering unit. However, a high DLS creates increased strain on the steering unit, causing some units to fail at the steering unit or, perhaps, on the drill string due to material fatigue.
Therefore, a need exists for a rotary steerable drilling assembly that offers an improved ability to redirect the force orientation of a drill bit during the drilling of a deviated wellbore at higher angles of deviation. Further, a need exists for a bottom hole assembly that, in some cases, employs electrical actuation rather than solely mechanical or hydraulic actuation for generating off-center, linear forces through a drill bit and against a rock formation.